The invention relates to a medical instrument with a hollow shaft having at its proximal end a handle consisting of at least two gripping members and at its distal end a tool consisting of at lest two jaw members, where at least one of the jaw members of the tool is adjustable in relation to the at least one other jaw member of the tool for purposes of opening and closing by means of one rotatably shaped gripping member of the handle, and the at least one adjustable jaw member and the corresponding gripping member of the handle that serves to adjust the jaw member are connected to one another by means of two push-pull rods.
Conventional instruments couple the movable jaw member or the movable jaw members by means of a lever mechanism. Here the angle between the instrument""s axis and the line through the pivot point of the jaw member and of the contact point on the lever is selected to be as wide as possible. In opening or closing the jaw members, the angle is forcibly reduced, however, and thus the transmission of power is clearly worsened. Particularly in medical punches for tissue, it is unclear what is the optimal angle of the jaw members that is required for transmitting power, since there can be various tissue thicknesses to deal with.
A conventional medical instrument is known from WO 98/1183 A2. In this familiar medical instrument configured as a forceps, the adjustable forceps member is connected with the rotatable gripping members of the handle by two push/pull rods, which are situated bilaterally on the rollers of a roller bearing, and the rollers are rigidly connected with the rotatable gripping member or the adjustable forceps member. The contact points of the push/pull rod are positioned on the roller of the adjustable forceps member in such a way that these points lie on a straight line above and below the pivot point of the adjustable forceps member, which straight line runs through the pivot point and these contact points.
Because of this 180-degree angle that extends between the two contact points along this straight line, it is inevitable that in the open or closed position of the adjustable forceps member, one of the angles applicable to the lever ratio must be clearly greater than 90 degrees between the longitudinal axis of the medical instrument and a line running through the pivot point of the adjustable forceps member and the contact points of the push/pull rods on the roller. The ideal lever ratio proves to be 90 degrees. The greater the anglexe2x80x94that is, the farther the force parallelogram is extendedxe2x80x94the more favorable are the lever ratios for transmitting power.
Another instrument is known from U.S. Pat. No. 4,712,545 A. In this familiar surgical instrument, the movable jaw member is conducted on a curved track in the stationary portion of the shaft and on an additional curved track toward the push pin. This configuration leads to imaginary pivot points that lie partly outside the instrument""s shaft. Through this method, however, only the lever arm is enlargedxe2x80x94similar effects can be achieved by such methods on the handlexe2x80x94and thus in every position more power is transmitted. However, the more the force parallelogram is extended, the more favorable the lever ratio becomes, so that in an extreme case even with a large lever arm no further power can be transmitted.
On the basis of this state of the art, the object of the invention is to make an improved medical instrument of the aforementioned type in such a way that it will ensure an always sufficient application of power onto the closing of the jaw members.
This object is achieved by means of the invention in that the two push/pull rods are secured on contact points at intervals from one another above and below the pivot point of the adjustable jaw member on this jaw member in such a way that two straight lines each extending from the pivot point through one of the contact points form an angle of 110 to 160 degrees.
Because the invention limits the angle between the two contact points to 110 to 160 degrees, it is possible to situate the position of the contact points of the push/pull rod on the adjustable jaw member and of the pivot point of the adjustable jaw member to one another in such a way that the angles alpha and beta between the longitudinal axis of, the medical instrument and a line through the contact points of the push/pull rod on the adjustable jaw member, both in the open position and also in the closed position, are each 90 degrees and thus ensure a virtually ideal lever ratio for a constantly sufficient transmission of power.
The result of this arrangement is that upon opening the jaw members, one push/pull rod is activated to push and the other rod to pull. Upon closing the jaw members, the functioning of the push/pull rod is correspondingly reversed. The use of one push/pull rod activated to push and one to pull also allows the penetration through tough tissue without the danger that an uncontrolled thrust occurs during penetration because of the sudden release of the resistance, since the transmission of power is always controllable because of the constantly favorable lever ratios.
In order to be able to clean the inventive medical instrument properly, and to make possible simple and rapid repairs, it is further proposed that the instrument should be constructed so that it can be dismantled.
In an initial embodiment of the invention, it is proposed that the push/pull roads should be dissolubly connected with the respective gripping member of the handle by means of a groove connection, in particular a spring-activated groove connection. In this manner the push/pull rods can then be pivoted out of the shaft together with the movable handle.
In another embodiment of the invention it is proposed that the tool should be secured on the distal end of the shaft by means of a bayonet coupling and the push/pull rods should be dissolubly attached on the movable gripping member.
In addition to using a common shaft for all push/pull rods, in an alternate embodiment it is proposed that every push/pull rod should be contained in a separate hollow shaft.
To reduce the rotation path of the gripping members of the handle toward one another, the handle can be equipped with a transmission so that the overall mobility of the instrument is increased.
Finally, it is proposed with this invention that the at least two jaw members of the tool should be configured to be adjustable by means of two push/pull rods each, so that each jaw member can be actuated by means of a separate gripping member of the handle. This configuration of the inventive medical instrument has the advantage that the jaw members can also be closed at various angle settings to the shaft.